To laymen, erosion control may seem like a straightforward problem, but it can quickly overwhelm site managers without the right information at their disposal.
Since no worksite is ever completely flat, dealing with gravity and sloping land can make your stormwater management controls a bit more complicated than you anticipated.
Not only does concentrating stormwater runoff to one or a few areas leave the ground vulnerable to increased erosion and sediment, but it also increases the risk of flooding and overwhelming drainage systems.
Establishing proper stormwater best management practices (BMPs) on slopes is one of the most essential parts of any stormwater management plan.
This guide will explain the intricacies of slope stormwater management and outline different techniques to improve your efforts.
The Importance of Slope Erosion Control
Simply put, slopes are particularly vulnerable to erosion as gravity naturally accelerates water and soil movement in these areas. Without proper stormwater management, sloped land and surfaces can suffer from:
- Loss of topsoil, reducing soil fertility and plant growth
- Increased sedimentation in waterways, harming aquatic ecosystems
- Water pooling, which can exacerbate the effects of erosion and sedimentation
- Structural damage to buildings, roads, and infrastructure if water collects near foundations
- Flooding of nearby areas if drainage systems become overwhelmed
- In extreme cases, dangerous landslides or mudslides
Ultimately stormwater management on slopes is important because it can reduce erosion of these areas, lead to easier revitalization, and protect nearby landscapes from the ill effects of increased runoff, such as flooding, pollution, sedimentation, or erosion.
Types of Erosion Site Managers Should Watch For
Sloped areas are particularly vulnerable to erosion from water and wind.
In the former instance, sheet erosion caused by large volumes of water can strip the top surface of the ground cover and dislodge loose soils underneath. At the foot of the slope, you also run the risk of rill or gully erosion, which is caused by excessive rainwater forming little gulleys or small tunnels in the soil, allowing water to pool.
Wind erosion can also impact bare and unprotected soil, allowing dust and dirt to pollute the local air and making establishing ground cover more difficult.
Therefore, site managers must take special consideration when accounting for slope erosion to accommodate the extra volume of rainwater and exposure to the elements.
11 Tips to Handle Stormwater Drainage on Slopes
1. Assess the Slope and Water Flow Patterns
Before implementing any drainage solutions, it is essential to perform an inspection of the entire site and analyze any slope’s gradient, soil type, and existing drainage patterns.
Observing how water flows during heavy rainfall can help identify areas prone to erosion, pooling, or excessive runoff. Conducting a site assessment will help determine the best stormwater management techniques for the specific slope.
2. Install Terracing or Retaining Walls
One of the most effective ways to manage stormwater on slopes is by creating terraces or retaining walls that help slow the movement of water and prevent erosion. These structures also allow for better water infiltration.
- Terracing involves constructing leveled steps along the slope, each acting as a mini retention basin to capture water. Terracing can provide a long-lasting and somewhat permanent solution to erosion problems.
- Retaining walls provide additional stability to prevent soil from washing away while also improving drainage when designed with weep holes or drainage pipes. Walls do require more maintenance over time as they are subject to cracking and fissuring from the natural movement of soils nearby.
3. Establish Vegetative Ground Cover
Planting vegetation is a natural and effective way to control erosion and manage stormwater runoff. Deep-rooted plants, shrubs, and grasses help stabilize the soil, reduce water velocity, and enhance water infiltration.
In instances where the land has been cleared or the top soils stripped, your site will require a fact-acting seeding solution to provide cover. Some permanent seeding solutions choices include:
- Hydroseeding: Consisting of a slurry mix of fertilizers, seeds, tackifiers, and other additives, this mixture can be sprayed across steep slopes using a special machine that provides fast-acting root establishment. Hydroseeding mixtures are available for grass and wildflowers.
- Mulching: Applying a thick layer of mulch across steep slopes can help establish fast seed growth and also protect the ground underneath from erosion in the meantime.
- Sodding: Commonly used on residential lawns, sodding helps provide immediate ground cover, while also creating a vibrant and hearty grass cover for long-lasting erosion control.
In addition, site managers can also plant ground cover plants, such as creeping junipers, vincas, shrubs, and native trees to protect bare slopes and slow the velocity of runoff.
4. Use Temporary Erosion Control Blankets
Temporary ground cover can help seeds grow and establish roots, while protecting the bare soil from erosion. Erosion control blankets are a popular solution, which consists of a geotextile fabric that protects the ground underneath while slowing the velocity of stormwater runoff. In addition, mulch and straw can also be used for temporary cover, though they may be more difficult to clean up.
5. Install Swales and Diversion Channels
Swales and diversion channels are shallow, gently sloped ditches designed to direct stormwater safely across a landscape. These features slow down runoff and redirect water to appropriate drainage points, such as retention basins or rain gardens, to prevent sloped hills from becoming overwhelmed with runoff. Consider lining swales with gravel, grass, or erosion-resistant materials to improve water absorption and stability.
6. Implement French Drains or Subsurface Drainage
Considered a more expensive and permanent solution, french drains can capture and redirect excess water underground without passing over the slope. They consist of perforated pipes buried in gravel trenches that collect and transport stormwater away from problem areas. Installing French drains along the slope can help prevent water buildup, reduce soil saturation, and minimize erosion risks.
7. Control Sediment with Silt Fences
In addition to erosion control, site managers must also account for sedimentation that can occur from sheet erosion and steep inclines. Silt fences not only capture heavy particles before leaving a worksite, but they can also provide some relief against erosion by slowing down the velocity of runoff and redirecting it to other areas of the site.
8. Use Permeable Paving and Check Dams
Impervious surfaces exacerbate runoff issues by preventing water infiltration. For example, if your worksite is located on a hill and has a sidewalk surrounding the perimeter, you can consider replacing it with a porous surface that absorbs water before discharging it downhill. Additionally, checking dams—small barriers placed at intervals along drainage channels—can help slow down water movement while promoting infiltration and reducing erosion.
9. Employ Ripraps Near Bodies of Water
If your worksite is located near a pond, stream, or riverbank, chances are that the surrounding perimeter of these water sources is sloped. To prevent excess erosion and potential sedimentation in these areas, consider installing ripraps and rockwalls around them to help slow runoff and filter out heavy particles.
10. Create Rain Gardens and Retention Basins
As previously mentioned, sheet erosion on hills is only one part of the problem we have to worry about. Preventing rill erosion at the base of the hill also requires special consideration.
Employing rain gardens and retention basins at the bottom of slopes could be a great solution to capture rainwater and filter out any heavy particles before discharging it off site.
- Rain gardens are shallow, planted depressions that absorb and filter runoff while beautifying the landscape.
- Retention basins collect stormwater temporarily, allowing it to slowly infiltrate the soil rather than causing immediate runoff.
Both methods help improve water quality and reduce the risk of erosion.
11. Inspect and Maintain Drainage Systems
Finally, routine maintenance is essential to ensure stormwater drainage systems function correctly. Clear debris from drains, check for signs of erosion and repair damaged infrastructure as needed. Regular inspections help identify potential issues before they escalate into costly problems.
For help drafting stormwater management solutions or actively inspecting your site, contact the exports at Valor Environmental to see how we can help.
FAQs
How can I slow down water runoff on a steep hill?
Installing check dams, terracing, planting deep-rooted vegetation, and using erosion control fabrics can all help slow down runoff and improve water absorption.
What are the best plants for erosion control on slopes?
Native grasses, ground cover plants like creeping juniper, and deep-rooted shrubs such as willows are great choices for stabilizing soil and reducing runoff.
How often should I maintain my stormwater drainage system?
Regular inspections should be done at least twice a year and after heavy storms to clear debris, check for erosion, and ensure proper drainage function.